Stabilized gold nanoparticles by reduction using 3,4-ethylenedioxythiophene-polystyrenesulfonate in aqueous solutions: nanocomposite formation, stability, and application in catalysis

Ultrasensitive, Label-Free Voltammetric Detection of Dibutyl Phthalate Based on Poly-l-lysine/poly(3,4-ethylenedioxythiophene)-porous Graphene Nanocomposite and Molecularly Imprinted Polymers

Development of an efficient technique for accurate and sensitive dibutyl phthalate (DBP) determination is crucial for food safety and environment protection. An ultrasensitive molecularly imprinted polymers (MIP) voltammetric sensor was herein engineered for the specific determination of DBP using poly-l-lysine/poly(3,4-ethylenedioxythiophene)/porous graphene nanocomposite (PLL/PEDOT-PG) and poly(o-phenylenediamine)-imprinted film as a label-free and sensing platform. Fabrication of PEDOT-PG nanocomposites was achieved through a simple liquid-liquid interfacial polymerization. Subsequently, poly-l-lysine (PLL) functionalization was employed to enhance the dispersibility and stability of the prepared PEDOT-PG, as well as promote its adhesion on the sensor surface. In the presence of DBP, the imprinted poly(o-phenylenediamine) film was formed on the surface of PLL/PEDOT-PG. Investigation of the physical properties and electrochemical behavior of the MIP/PLL/PEDOT-PG indicates that the incorporation of PG into PEDOT, with PLL uniformly wrapping its surface, significantly enhanced conductivity, carrier mobility, stability, and provided a larger surface area for specific recognition sites. Under optimal experimental conditions, the electrochemical response exhibited a linear relationship with a logarithm of DBP concentration within the range of 1 fM to 5 µM, with the detection limit as low as 0.88 fM. The method demonstrated exceptional stability and repeatability and has been successfully applied to quantify DBP in plastic packaging materials.

Enhanced Stability and Catalytic Activity of a Nanocatalyst with Reusable Ionic Liquid Hydrogels for the Reduction of Organic Pollutants

Nitroaromatic compounds have a wide range of applications. However, they pose a significant threat to both the environment and human health. Ionic liquid hydrogels (ILs-gels) have emerged as a cost-effective and environmentally friendly option for various applications. However, conventional ILs-gels are known to possess mechanical flaws or defects. The procedure utilized a facile synthesis route that involved the polymerization of acrylamide (AM) and ionic liquids (ILs) to create a novel candidate for nanoparticle absorption. This study resolved this issue by creating toughened hydrophobic combined hydrogels synthesized through the addition of SiO2@poly(butyl acrylate) core-shell inorganic-organic hybrid latex particles (SiO2@PBA) to the AM-ILs mixture. The SiO2@PBA particles were chosen to provide the hydrogels with exceptional stretchability (up to 4050% strain) and high mechanical properties (tensile strength of 126 kPa) by acting as both a nanotoughener and a cross-linking point for hydrophobic linkage. Additionally, the P(AM/ILs)-SiO2@PBA hydrogel served as a template for the in situ and stable formation of palladium (Pd) nanoparticles. By incorporation of these Pd nanoparticles as catalysts into P(AM/ILs)-SiO2@PBA hydrogel carriers, the resulting P(AM/ILs)-SiO2@PBA/Pd hydrogels exhibited the ability to catalyze the degradation of p-nitrophenol. Remarkably, even after 15 applications, the efficiency of the degradation process remained consistently above 90%. Thus, the innovative SiO2@PBA toughened ILs-hydrogel design strategy can be utilized to develop robust and stretchable hydrogel materials for catalytic use in the sewage disposal industry.

Photocatalytic Water-Splitting by Organic Conjugated Polymers: Opportunities and Challenges

The future challenges associated with the shortage of fossil fuels and their current environmental impacts intrigued the researchers to look for alternative ways of generating green energy. Solar-driven water splitting into oxygen and hydrogen is one of those advanced strategies. Researchers have studied various semiconductor materials to achieve potential results. However, it encountered multiple challenges such as high cost, low photostability and efficiency, and required multistep modifications. The conjugated polymers (CPs) have emerged as promising alternatives for conventional inorganic semiconductors. The CPs offer low cost, sufficient light absorption efficiency, excellent photo and chemical stability, and molecular optoelectronic tunable characteristics. Furthermore, organic CPs also present higher flexibility to tune the basic framework of the backbone of the polymers, amendments in the sidechain to incorporate desired functionalities, and much-needed porosity to serve better for photocatalytic applications. This review article summarizes the recent advancements made in visible-light-driven water splitting covering the aspects of synthetic strategies and experimental parameters employed for water splitting reactions with special emphasis on conjugated polymers such as linear CPs, planarized CPs, graphitic carbon nitride (g-C₃ N₄ ), conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), and conjugated polymer-based nanocomposites (CPNCs). The current challenges and future prospects have also been described briefly.

A novel Au/electroactive poly(amic acid) composite as an effective catalyst for p-nitrophenol reduction

A Au/electroactive poly(amic acid) (Au/EPAA) composite was synthesized and characterized, and its catalytic ability was evaluated. EPAA was synthesized via oxidative coupling polymerization and Au nanoparticles were anchored to the amino and carboxyl groups. The Au/EPAA composite was characterized via X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy, which confirmed that the Au nanoparticles were well dispersed on the EPAA surface. p-Nitrophenol was reduced to p-aminophenol within 5 min at room temperature, with a rate constant of 0.84 min⁻¹. Cycling measurements showed that the Au/EPAA composite achieved higher than 92% conversion. The Au/EPAA composite showed excellent performance and stability as a catalyst for the reduction of p-nitrophenol to p-aminophenol.

The Au/EPAA composite demonstrated excellent performance and stability as a catalyst for the reduction of p-nitrophenol to p-aminophenol.

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) shell) nanostructures and their monolayer arrays for plasmonic switching

(Gold nanorod core)/(poly(3,4-ethylene-dioxythiophene) (PEDOT) shell) nanostructures are prepared by the surfactant-assisted oxidative polymerization of 3,4-ethylene-dioxythiophene on the surface of gold nanorods (NRs). The PEDOT shell exhibits distinct dielectric properties at doped and undoped states, which allows the manipulation of plasmonic responses of the Au nanorod core. The shift in plasmon resonance induced by the dedoping of PEDOT is found to be associated with the overlap between the plasmon resonance band of the core/shell nanostructure and the spectral region where the largest refractive index variation of PEDOT occurs, as well as with the type of the dedopant. Macroscopic two-dimensional (2D) monolayer arrays of core/shell nanostructures with controlled particle number densities are fabricated on indium tin oxide (ITO)-coated glass substrates by electrophoretic deposition. A reversible plasmonic shift of about 70 nm is obtained on the core/shell nanostructure monolayer array with a number density of around 18 particles per μm2. Our design of colloidal (Au nanorod core)/(PEDOT shell) nanostructures and their 2D monolayer arrays paves the way for the fabrication of high-performance plasmonic switches in large-scale practical usages as well as for the preparation of advanced, programmable chromic materials for a broad range of applications, such as smart windows, anti-counterfeiting tags, and medical and environmental sensors.

A simple electrochemical approach to fabricate functionalized MWCNT-nanogold decorated PEDOT nanohybrid for simultaneous quantification of uric acid, xanthine and hypoxanthine

Medical diagnostics and detection of food spoilage require estimation of hypoxanthine (HX), xanthine (XN), and uric acid (UA). A selective sensing platform has been proposed for simultaneous detection of all these species. Functionalized multi-walled carbon nanotube (fMWCNT) stabilized nanogold decorated PEDOT:TOS polymeric nanocomposite (Au-PEDOT-fMWCNT) was synthesized through rapid one-step electropolymerization to enhance conductivity and active surface area by several folds. Electrochemical activities of the proposed sensing platform were analyzed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS). Analyses through SEM, FESEM and TEM were performed to explore the surface morphology and elemental analysis of the polymeric nanohybrid was investigated by XPS, Raman, FTIR, XRD spectroscopy. Electro-catalysis of UA, XN and HX occurred at low oxidation potentials i.e. 0.082, 0.463 and 0.808 V, respectively in the optimized conditions. The uniquely designed simple, interference free Au-PEDOT-fMWCNT/GCE sensor exhibited high selectivity, good reproducibility, reusability (∼180 times) and stability (∼3 month) with excellent sensitivity of 1.73, 14.31 and 3.82 μA μM^-1 cm^-2 for UA, XN and HX, respectively. The sensor exhibited linear ranges of detection as 0.1-800, 0.05-175 and 0.1-150 μM with detection limits of 199.3, 24.1 and 90.5 nM for quantification of UA, XN and HX respectively. The performance of the proposed sensor was validated by addition of UA, XN and HX in human serum, urine and fish samples by comparing to those using HPLC. The results indicated good applicability of the proposed sensor for simultaneous detection of UA, XN, HX in real biological fluids.

Drying of electrically conductive hybrid polymer-gold nanorods studied with in situ microbeam GISAXS

Gold nanorods (AuNRs) with conductive polymer shells are interesting colloidal building blocks for electronics. Hybrid particles with AuNR cores and poly(3,4-ethylenedioxythiophene) or polystyrene sulfonate (PEDOT:PSS) shells were prepared as stable aqueous dispersions. Film formation during the drying of such dispersions is known to affect the electric conductivity of the material. We observed the mechanisms of drying in thin, spray-coated films with grazing incidence small-angle X-ray scattering (GISAXS). A sparse, uniform monolayer formed because the anisotropic shape of the AuNR inhibited "coffee-ring" effects. We used generalized two-dimensional correlation (2DC) spectroscopy to analyze the GISAXS data and to decipher the microscopic structure formation of the film during drying. Four major scattering peaks were attributed to porous PEDOT, PSS, Au, and the substrate layer. Their time-dependent intensity indicated the sequence of film formation: AuNRs with mobile shells arranged on the substrate first, and PEDOT and then PSS dried sequentially around the gold core. We discuss the final phase-separation of PEDOT:PSS on the hybrid rods.

Nitrogen-containing polymers as a platform for CO2 electroreduction

Heterogeneous electroreduction of CO₂ has received considerable attention in the past decade. However, none of the earlier reviews has been dedicated to nitrogen-containing polymers (N-polymers) as an emerging platform for conversion of CO₂ to industrially useful chemicals. The term 'platform' is used here to underscore that the role of N-polymers is not only to serve as direct catalysts (through loaded metals) but also as co-catalysts/promoters and stabilizing agents. This review covers the current state, advantages, challenges, and prospects of the application of N-polymer-metal composites, also referred as polymer functionalized, coated, or modified electrodes, as well as functional hybrid materials, for the electrocatalytic conversion of CO₂. It briefly surveys the efficiencies of the N-polymer-metal electrodes already used for this application, methods of their fabrication, and proposed mechanisms of their catalytic activities.

Gold nanoparticle-polymer nanocomposites synthesized by room temperature atmospheric pressure plasma and their potential for fuel cell electrocatalytic application

Conductive polymers have been increasingly used as fuel cell catalyst support due to their electrical conductivity, large surface areas and stability. The incorporation of metal nanoparticles into a polymer matrix can effectively increase the specific surface area of these materials and hence improve the catalytic efficiency. In this work, a nanoparticle loaded conductive polymer nanocomposite was obtained by a one-step synthesis approach based on room temperature direct current plasma-liquid interaction. Gold nanoparticles were directly synthesized from HAuCl₄ precursor in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The resulting AuNPs/PEDOT:PSS nanocomposites were subsequently characterized under a practical alkaline direct ethanol fuel cell operation condition for its potential application as an electrocatalyst. Results show that AuNPs sizes within the PEDOT:PSS matrix are dependent on the plasma treatment time and precursor concentration, which in turn affect the nanocomposites electrical conductivity and their catalytic performance. Under certain synthesis conditions, unique nanoscale AuNPs/PEDOT:PSS core-shell structures could also be produced, indicating the interaction at the AuNPs/polymer interface. The enhanced catalytic activity shown by AuNPs/PEDOT:PSS has been attributed to the effective electron transfer and reactive species diffusion through the porous polymer network, as well as the synergistic interfacial interaction at the metal/polymer and metal/metal interfaces.

Electrochemical and optical bimodal sensing of caffeic acid based on electrodes made from nanorods of AuNPs:PEDOT:PSS and bio-hybrid chitosan:PEDOT:PSS

One pot in situ synthesis of AuNPs:PEDOT:PSS using a green solvent and its utilization as an electrochemical sensor.

Preparation and catalytic activity of magnetic bimetallic nickel/copper nanowires

Nowadays, 4-nitrophenol (4-NP), one of the most toxic pollutants of waste water, is capturing more attention in the field of sewage disposal.

Polythiophene/graphene oxide nanostructured electrodeposited coating for on-line electrochemically controlled in-tube solid-phase microextraction

In this work, a novel polythiophene/graphene oxide (PTh/GO) nanostructured coating was introduced for on-line electrochemically-controlled in-tube solid phase microextraction of amitriptyline (AMI) and doxepin (DOX) as antidepressant drugs. The PTh/GO coating was prepared on the inner surface of a stainless steel tube by a facile in-situ electro-deposition method and it was used as a working electrode for electrochemically control in-tube solid phase microextraction. In the PTh/GO coating, GO acts as an anion dopant and sorbent. The PTh/GO coating, compared to PTh and GO coatings, exhibited enhanced long lifetime, good mechanical stability and a large specific surface area. Regarding the in-tube SPME, some important factors such as the extraction and desorption voltage, extraction and desorption times and flow rates of the sample solution and eluent, which could affect the extraction and separation efficiency of the analytes, were optimized. Total analysis time of this method including the online extraction and desorption time was about 21min for each sample. AMI and DOX were extracted, separated and determined with limits of detection as small as 0.3μgL^-1 and 0.5μgL^-1, respectively. This method showed good linearity in the range of 0.7-200μgL^-1, 2.3-200μgL^-1 and 2.9-200μgL^-1 for AMI, and in the range 0.9-200μgL^-1, 2.5-200μgL^-1 and 3.0-200μgL^-1 for DOX in water, urine and plasma samples, respectively; the coefficients of determination were also equal to or higher than 0.9976. The inter- and intra-assay precisions (RSD%, n=3) were in the range of 2.8-3.4% and 2.9-3.9% at the three concentration levels of 5, 25 and 50μgL^-1, respectively. Finally, under the optimal conditions, the method was applied for the analysis of the drugs in human urine and plasma pretreated samples and good results were obtained.

Nanostructured conducting polymers for energy applications: towards a sustainable platform

Recently, there has been tremendous progress in the field of nanodimensional conducting polymers with the objective of tuning the intrinsic properties of the polymer and the potential to be efficient, biocompatible, inexpensive, and solution processable. Compared with bulk conducting polymers, conducting polymer nanostructures possess a high electrical conductivity, large surface area, short path length for ion transport and superior electrochemical activity which make them suitable for energy storage and conversion applications. The current status of polymer nanostructure fabrication and characterization is reviewed in detail. The present review includes syntheses, a deeper understanding of the principles underlying the electronic behavior of size and shape tunable polymer nanostructures, characterization tools and analysis of composites. Finally, a detailed discussion of their effectiveness and perspectives in energy storage and solar light harvesting is presented. In brief, a broad overview on the synthesis and possible applications of conducting polymer nanostructures in energy domains such as fuel cells, photocatalysis, supercapacitors and rechargeable batteries is described.

Structure and effects of gold nanoparticles in bacterial cellulose–polyaniline conductive membranes

Bacterial cellulose (BC) and poly(aniline) (PANI) composites were successfully synthesized by in situ polymerization of aniline by ammonium persulphate (APS) in the presence and absence of gold nanoparticles.

Ultrastable-Stealth Large Gold Nanoparticles with DNA Directed Biological Functionality

The stability of gold nanoparticles (AuNPs) in biological samples is very important for their biomedical applications. Although various molecules such as polystyrenesulfonate (PSS), phosphine, DNA, and polyethylene glycol (PEG) have been used to stabilize AuNPs, it is still very difficult to stabilize large AuNPs. As a result, biomedical applications of large (30-100 nm) AuNPs are limited, even though they possess more favorable optical properties and are easier to be taken up by cells than smaller AuNPs. To overcome this limitation, we herein report a novel method of preparing large (30-100 nm) AuNPs with a high colloidal stability and facile chemical or biological functionality, via surface passivation with an amphiphilic polymer polyvinylpyrrolidone (PVP). This PVP passivation results in an extraordinary colloidal stability for 13, 30, 50, 70, and 100 nm AuNPs to be stabilized in PBS for at least 3 months. More importantly, the PVP capped AuNPs (AuNP-PVP) were also resistant to protein adsorption in the presence of serum containing media and exhibit a negligible cytotoxicity. The AuNP-PVPs functionalized with a DNA aptamer AS1411 remain biologically active, resulting in significant increase in the uptake of the AuNPs (∼12,200 AuNPs per cell) in comparison with AuNPs capped by a control DNA of the same length. The novel method developed in this study to stabilize large AuNPs with high colloidal stability and biological activity will allow much wider applications of these large AuNPs for biomedical applications, such as cellular imaging, molecular diagnosis, and targeted therapy.

Nitroarene reduction: a trusted model reaction to test nanoparticle catalysts

Nitrophenol reduction to aminophenol with a reducing agent is conveniently carried out in aqueous medium mainly with a metal or metal oxide catalyst. This reduction is presently considered as a benchmark reaction to test a catalyst nanoparticle. Thousands of original reports have enriched this field of nanoparticle catalyzed reaction. Synthesis of different metal and metal oxide nanoparticles and their composites along with their role as catalysts for nitrophenol reduction with varying reducing agents have been elucidated here. The progress of the reaction is conveniently monitored by UV-visible spectrophotometry and hence it becomes a universally accepted model reaction. In this review we have discussed the reaction kinetics considering its elegance and importance enlightening the long known Langmuir-Hinshelwood mechanism and Eley-Rideal mechanism at length, along with a few other mechanisms recently reported. A brief description of the synthetic procedures of various nanoparticles and their respective catalytic behaviour towards nitroarene reduction has also been accounted here.

Exploring metal nanoclusters for lithium-oxygen batteries

α-MnO2 nanowires modified with dispersed poly(3,4-ethylenedioxythiophene)-protected Au and Ag nanoclusters (Au-MnO2 and Ag-MnO2) were used for the first time as hybrid oxygen electrocatalysts for nonaqueous lithium-oxygen batteries. The Au-MnO2 and Ag-MnO2 hybrid catalysts surpassed the performance of pristine α-MnO2 nanowires in full-cell tests in the following order: Au-MnO2 > Ag-MnO2 > pristine α-MnO2. Specifically, cells with the Au-MnO2 catalyst could reduce the discharge/charge overpotentials at 100 mA g(-1) to 0.23/1.02 V and deliver discharge/charge capacities of 5784/5020 mAh g(-1). They could also be cycled for at least 60 times at the depth of discharge of 1000 mAh g(-1). The good full cell performance demonstrated the effectiveness of Au/Ag nanoclusters in promoting oxygen electrocatalysis on α-MnO2; forming discharge products with more reactive morphologies. It is therefore worthwhile to explore the use of Au and Ag nanoclusters in other catalyst systems for oxygen electrocatalysis in nonaqueous solutions.

Parallel synthesis of poly(amino ether)-templated plasmonic nanoparticles for transgene delivery

Plasmonic nanoparticles have been increasingly investigated for numerous applications in medicine, sensing, and catalysis. In particular, gold nanoparticles have been investigated for separations, sensing, drug/nucleic acid delivery, and bioimaging. In addition, silver nanoparticles demonstrate antibacterial activity, resulting in potential application in treatments against microbial infections, burns, diabetic skin ulcers, and medical devices. Here, we describe the facile, parallel synthesis of both gold and silver nanoparticles using a small set of poly(amino ethers), or PAEs, derived from linear polyamines, under ambient conditions and in absence of additional reagents. The kinetics of nanoparticle formation were dependent on PAE concentration and chemical composition. In addition, yields were significantly greater in case of PAEs when compared to 25 kDa poly(ethylene imine), which was used as a standard catonic polymer. Ultraviolet radiation enhanced the kinetics and the yield of both gold and silver nanoparticles, likely by means of a coreduction effect. PAE-templated gold nanoparticles demonstrated the ability to deliver plasmid DNA, resulting in transgene expression, in 22Rv1 human prostate cancer and MB49 murine bladder cancer cell lines. Taken together, our results indicate that chemically diverse poly(amino ethers) can be employed for rapidly templating the formation of metal nanoparticles under ambient conditions. The simplicity of synthesis and chemical diversity make PAE-templated nanoparticles useful tools for several applications in biotechnology, including nucleic acid delivery.

Surfactant-free nanoparticle–DNA complexes with ultrahigh stability against salt for environmental and biological sensing

A AuNP–DNA complex highly stable in extremely high ionic strength media, such as seawater, was obtained by inserting a few thymine bases into the DNA strands.

Facile solvothermal preparation of monodisperse gold nanoparticles and their engineered assembly of ferritin-gold nanoclusters

Herein, we report a quick and simple synthesis of water-soluble gold nanoparticles using a HAuCl4 and oleylamine mixture. Oleylamine serves as a reduction agent as well as a stabilizer for nanoparticle surfaces. The particle sizes can be adjusted by modulating reaction temperature and time. Solvothermal reduction of HAuCl4 with oleylamine can be confirmed by measuring the product in Fourier transform infrared (FTIR) spectroscopy. The plasmon band shifting from yellow to red confirms a nanosized particle formation. Amide bonds on the surface of the nanoparticles formed hydrogen bonds with one another, resulting in a hydrophobic monolayer. Particles dispersed well in nonpolar organic solvents, such as in hexane or toluene, by brief sonication. Next, we demonstrated the transfer of gold nanoparticles into water by lipid capsulation using 1-myristoyl-2-hydroxy-sn-glycero-3-phosphocholine (MHPC), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy polyethylene glycol)-2000 (DPPE-PEG2k), and 1,2-dioleoyl-sn-glycero-3-N-{5-amino-1-carboxypentyl}iminodiacetic acid succinyl nickel salt [DGS-NTA(Ni)]. The particle concentration can be obtained using an absorbance in ultraviolet-visible (UV-vis) spectra (at 420 nm). Instrumental analyses using transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis, dynamic light scattering (DLS), and FTIR confirmed successful production of gold nanoparticles and fair solubility in water. Prepared gold particles were selectively clustered via engineered ferritin nanocages that provide multiple conjugation moieties. A total of 5-6 gold nanoparticles were clustered on a single ferritin nanocage confirmed in TEM. Reported solvothermal synthesis and preparation of gold nanoclusters may serve as an efficient, alternate way of preparing water-soluble gold nanoparticles, which can be used in a wide variety of biomedical applications.

A two-stage enzymatic synthesis of conductive poly(3,4-ethylenedioxythiophene)

The conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), possesses attractive properties that show the potential applications in many fields. In this study, we have proposed a two-stage enzymatic synthesis of conductive PEDOT. Horseradish peroxidase (HRP) acts as the catalyst to promote the generation of EDOT free radicals followed by the polymerization under the room temperature in the presence of poly(sodium 4-styrenesulfonate) (PSS), then a mild heating process is employed for further chain extension. The final PEDOT:PSS is purified with n-butanol and subjected to various characterizations, which indicate that PEDOT with enzymatic approach exhibits a similar molecular structure to that with chemical method. However, the enzymatically synthesized PEDOT:PSS demonstrates advantages, such as stable integration of PEDOT with PSS and better electrochemical properties, suggesting its future prospective applications.

One-pot synthesis of poly (3,4-ethylenedioxythiophene)-Pt nanoparticle composite and its application to electrochemical H2O2 sensor

Poly(3,4-ethylenedioxythiophene)-Pt nanoparticle composite was synthesized in one-pot fashion using a photo-assisted chemical method, and its electrocatalytic properties toward hydrogen peroxide (H2O2) was investigated. Under UV irradiation, the rates of the oxidative polymerization of EDOT monomer along with the reduction of Pt4+ ions were accelerated. In addition, the morphology of PtNPs was also greatly influenced by the UV irradiation; the size of PtNPs was reduced under UV irradiation, which can be attributed to the faster nucleation rate. The immobilized PtNPs showed excellent electrocatalytic activities towards the electroreduction of hydrogen peroxide. The resultant amperometric sensor showed enhanced sensitivity for the detection of H2O2 as compared to that without PtNPs, i.e., only with a layer of PEDOT. Amperometric determination of H2O2 at -0.55 V gave a limit of detection of 1.6 μM (S / N = 3) and a sensitivity of 19.29 mA cm-2 M-1 up to 6 mM, with a response time (steady state, t95) of 30 to 40 s. Energy dispersive X-ray analysis, transmission electron microscopic image, cyclic voltammetry (CV), and scanning electron microscopic images were utilized to characterize the modified electrode. Sensing properties of the modified electrode were studied both by CV and amperometric analysis.

Facile and one pot synthesis of gold nanoparticles using tetraphenylborate and polyvinylpyrrolidone for selective colorimetric detection of mercury ions in aqueous medium

In this work, we reported for the first time, a facile and one step synthesis of gold nanoparticles from HAuCl(4), employing tetraphenylborate as the reducing agent. The synthesis is not only facile but also yields "dumb-bell-shaped"particles. This shape appears to arise from a possible emulsion of the products of oxidation/decomposition of tetraphenylborate by HAuCl(4), surrounding the particle. The size and shape of the AuNPs were characterized by Transmission electron microscopy (TEM) and UV-visible Spectroscopy. Interestingly, the addition of polyvinylpyrrolidone (PVP) during the synthesis was found to enhance the stability of the nanoparticle dispersion. The particles synthesized under these conditions assume "spherical" shape with the appearance of only transverse surface plasmon resonance band. The highlight of the observations is that the gold nanoparticles synthesized using tetraphenylborate as reducing agent and PVP as stabilizer are highly stable in alkaline medium, in contrast to the synthesis wherein borohydride is used as reducing agent. The AuNPs synthesized using tetraphenylborate and PVP show their mercury sensing behavior only in the alkaline medium. The color of the nanoparticle dispersion undergoes distinct color change from pink to blue with the addition of mercury ions. They also show dramatic selectivity to mercury ions in presence of other interfering ions, Pb(2+), Zn(2+) and Ca(2+).

4-(Dimethylamino)pyridine as a powerful auxiliary reagent in the electroless synthesis of gold nanotubes

Gold nanotubes of small particle sizes down to 5 nm and high aspect ratios were synthesized in ion track etched polycarbonate following a rational reaction design. 4-(Dimethylamino)pyridine (DMAP) was employed to adjust the electroless deposition by interfering with the autocatalytically active gold surface. Modification of the pH value and DMAP concentration led to a wide range of products which were characterized by SEM, TEM, and EDS. Filigree nanotubes of 10-15 nm wall thickness and 5.0 ± 2.1 nm grain size were obtained as well as robust and free-standing structures proving homogeneous deposition along the whole template length of 30 μm. Template-supported gold nanotubes were applied in the UV-vis monitored reduction of 4-nitrophenol by sodium borohydride under pseudo-first-order conditions. They proved to be a reliable microfluidic system of excellent catalytic activity coming up with an apparent rate constant of 1.3 × 10(-2) s(-1). Despite a high flow rate, the reaction showed 99% conversion after a distance of just 60 μm.